In a conventional inkjet printer, a printhead has a series of droplet apertures or nozzles out of which the printing fluid or ink ejects to an image receiving substrate. Each nozzle can have a corresponding actuator for ejecting the ink through the nozzle. The ink drop mass, or size, and drop speed, or velocity, can influence the quality of the printing. For example, the drop mass and speed can affect drop placement and satellite formation. In inkjet printers with a constant diameter (cylindrical) nozzle, both the ejected ink drop mass and drop speed are dependent on nozzle diameter. For example, an increase in nozzle diameter increases both the drop mass and drop speed of the ejected ink. As such, complicated design optimizations are undertaken to attempt to obtain an acceptable drop speed in conjunction with a desired drop mass.
As are known in the art, conventional tapered, or conical, nozzles can be used instead of cylindrical nozzles. The exit diameter of the conventional tapered nozzle, or the point at which the ink drop exits the nozzle, can be used to adjust drop mass. Further, the conventional tapered nozzle can increase drop speed and improve alignment tolerances. However, conventional tapered nozzle designs cannot maintain independent control of both the drop mass and the drop speed.
In liquid droplet ejecting devices with a constant diameter aperture (cylindrical nozzle) both the ejected drop size and drop speed are dependent on the aperture diameter. The aperture diameter is a commonly known element used to adjust the drop mass. The high degree of correlation in the drop mass and drop velocity means that complicated design optimizations involving many of the single jet parameters must be undertaken to obtain an acceptable drop velocity simultaneous with the desire drop mass. It would, therefore, be desirable to separate the adjustment in drop mass form the adjustment in drop velocity.
Thus, there is a need for a stepped nozzle design which can control the ink drop mass independently of the drop speed and reduce the need for complicated design optimizations.